O020 Can bacteria survive in PAP airflow: a conceptual benchtop study

Abstract Introduction It is unknown if positive airway pressure (PAP) devices are a potential reservoir of infectious microbes. We aimed to develop air sampling methodology for a PAP device under pressurised conditions, and to validate it using a limit of detection (LoD) technique, with concurrent viability and molecular assessment. Methods Exploratory methodology was used to assess pressurised airflow from PAP devices under conditions of intentional contamination with Pseudomonas aeruginosa (PA) or Escherichia coli (EC). Comparison between Anderson Cascade Impactor and a simple underwater broth methodology occurred for feasibility. The LoD methodology was used to find the lowest concentration of bacteria that was recoverable on culture (growth) vs molecular (16S rRNA gene sequencing) to ascertain detection of bacteria below the threshold of growth. Then, deliberate inoculation of device sites with PA was used to model the inhalation hazard of real-world contamination (air inlet, outlet, humidifier, and post-machine circuit). Results A model using intra-circuit nebulised bacteria determined LoD at 0.5McF (1.5 x 10^8 CFU/ml) for EC and 1.5 x 10^7 CFU/mL for PA. No viable cultures were detected at concentrations below the threshold of detection, or by inoculation at various device sites. Detection of airborne bacteria was only possible using nebulisation of organism in high concentrations unlikely to occur in real-world situations. Discussion Under normal operating conditions, recovery of viable bacteria did not occur. Hostility of airflow conditions may govern the non-viability of identified molecular isolates below the LoD. This study demonstrates non-survivability of two common bacteria with clinically relevant PAP settings.